Graphene nanoribbons lower power, cooler than copper

PORTLAND, Ore.Graphene will carry nearly 1,000-times more current and run over 10-times cooler than conventional copper interconnects below 22-nanometer line widths, according to researchers at the Georgia Institute of Technology (Georgia Tech).

The speed (electron mobility) of graphene has already been touted as better than copper, but this Georgia Tech data on nanoribbons as small as 16-nanometers quantifies just how superior carbon is to copper. The graphene nanoribbons tested at Georgia Tech could carry as much as 10 billion amps per square centimeternearly a thousand times greater than copper.

"No one had measured graphene's current carrying capacity before this," said Raghunath Murali, a senior research engineer in Georgia Tech's Nanotechnology Research Center. "One possible reason that this property of graphene was not touted before is that there were no experimental results until our work."

The superior current carrying capability of carbon formed into graphene nanoribbons is also combined with less heat build-up, since carbon's thermal conductivity is much higher than copper. Nanoribbons have a thermal conductivity of 1,000-to-5000 watts per meter Kelvinten times greater than copper. The Georgia Tech researchers also claim that graphene nanoribbons will mitigate electro-migration which is an increasing problem for copper as line widths descend to the nanoscale.

"If the current carried through a wire is close to the current-carrying capacity of the wire, then the chances of electromigration are greater than if the current in the wire is much smaller than the current-carrying capacity," said Murali. "Graphene has over two orders of magnitude greater capacity than copper, thus if a graphene wire is compared to a copper wire carrying the same current, then the graphene wire will better resist electromigration."

Murali's team obtained their graphene samples by removing layers from a graphite block and depositing them on a silicon-on-insulator (SOI) wafer. E-beam lithograhy was used to construct the metal contacts and cut the parallel lines of graphene into lines 16-to-52 nanometers wide and 200-to-1000 nanometers long.

There are three hurdles remaining to commercialization of carbon interrconnects, according to the researchers at Georgia Tech: perfecting methods of growing monolayers of graphene over entire wafers (since today only small centimeter-sized areas can be easiliy grown in monolayers), fabricating vias to interrconnect graphene nanowires, and integration of carbon into the back-end of process on a CMOS line.

Murali performed the work with fellow researchers Yinxiao Yang, Kevin Brenner, Thomas Beck and James Meindl. This research was funded by the Semiconductor Research Corporation, the Defense Advanced Research Projects Agency (DARPA), the Interconnect Focus Center, the Nanoelectronics Research Initiative and the Institute for Nanoelectronics Discovery and Exploration (INDEX).